In perpendicular magnetic recording the data is recorded on a magnetic disk in which the easy axis of magnetization is aligned perpendicular to the surface of the disk. The recording head, viewed from the air bearing surface, contains a relatively small main pole and a relatively large auxiliary pole.
The recording head is normally mounted on a rotary arm which pivots about a stationary axis to move the head to various radial positions on the disk. This generates a skew angle θ between the main axis of the rotary arm and the tangential direction of the data tracks on the disk. This is illustrated schematically in FIGS. 1A-1C. In FIG. 1A the skew angle θ is equal to zero, i.e., the main axis of rotary arm 2 is exactly parallel to the data track on disk 4 that underlies the recording head 3 at the end of rotary arm 2. In FIG. 1B, where the recording had 3 is located nearer to the center of disk 4, the skew angle is equal to θ1. In FIG. 1C, where recording head 3 is located nearer to the edge of disk 4, the skew angle is equal to θ2 (which would have a sign opposite to that of θ1).
The existence of a skew angle creates the problem illustrated in FIG. 2A, which is a schematic top view of the main pole 5 over two data tracks T1 and T2. The skew angle is θ3. Although recording head 5 is writing to track T2, it is evident that a corner of head 5 overlies track T1. A solution to this problem is to fabricate the recording head with a trapezoidal shape, as shown in FIG. 2B. As shown, recording head 6 does not extend over track T1 when the skew angle is equal to θ3 because the sides of head 6 are canted by an angle α, giving head 6 a trapezoidal shape.
FIG. 3 is general schematic view of a perpendicular recording head 10 taken from the air-bearing surface (ABS), showing a main pole 11, an auxiliary pole 12, a reading element 13 and a lower shield 14. For clarity, the components shown in FIG. 3 are not drawn to scale. The sides of main pole 11 are beveled by an angle α. It should be noted that this invention does not involve the structure of the auxiliary pole, reading element or lower shield. These components are well known and can be fabricated in accordance with known techniques.
FIG. 4 is a view of recording head 10 taken through a cross section that is perpendicular to the ABS. Shown are the main pole 11 and the auxiliary pole 12. Also shown are a yoke 15, a back gap 16 and a coil 17. The main pole 11, auxiliary pole 12, yoke 15 and back gap 16 are made of a magnetic metal such as NiFe. The coil 16 is made of an electrically conductive metal such as Cu. The supporting layers separating these components are made of a hard nonconductive material such as alumina (Al2O3). In operation, an electrical signal through coil 17 generates a magnetic flux that flows through yoke 15 and main pole 11 in the direction of the ABS and from the head to a magnetic recording disk (not shown).
FIGS. 5A and 5B are views of main pole 11 from the ABS and show how the trapezoidal shape is normally fabricated. Initially, main pole 11 has a rectangular shape, as shown in FIG. 5A. An ion milling process is normally used to bevel the sides of main pole 11. As indicated by the arrows, the ion beam is directed to main pole 11 at an oblique angle so as to erode more material near the bottom of main pole 11. To erode both sides of the main pole, the ion beam can be programmed to change the angle of incidence in sequence.
FIG. 6 is a close-up view of the area designated A in FIG. 4, which is where most of the discussion herein is directed. The interface between the yoke 15 and the main pole 11 is shown, as well as the underlying and overlying alumina layers. The arrows denote the magnetic flux flowing from the yoke 15 to the main pole 11 and to the ABS.
One of the difficulties that has been encountered is to get a large enough bevel angle α in the main pole to avoid the problems of cross talk and signal-to-noise (STN) degradation described above. Conventionally, the layer directly below the main pole is made of alumina, which is a very hard material. The presence of this underlying alumina layer acts as a hard mask from below and makes it difficult to get a large bevel angle with the ion milling process. This can happen in two ways. First, the alumina layer retards the material of the main pole from being removed without over-milling. Second, during the milling process the alumina may redeposit onto the surfaces of the main pole, slowing down the removal process even more.